I would also think this. And would also repeat @Morgan_Hardwood’s question.
@charlyw64: I also have to add, that I don’t recall the original image being that noisy/grainy. It stems from 7 exposure blended using hugin, and if memory serves me correctly each single pictures was taken at ISO100 or in the worst case at ISO400. So there shouldn’t be much noise.
I did however use the resize function in RT and the post resize sharpening just to make the pictures smaller for upload, and did not control what the result looked like. I will look at the original picture later to see where the noise comes from, as I’m curious.
But still, I think the tool works perfectly also with non noisy pictures.